INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING

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The paper was published in the proceedings of the 25th European Young Geotechnical Engineers Conference and was edited by Ernest Olinic and Sanda Manea. The conference was held in Sibiu, Romania 21-24 June 2016.

25th European Young Geotechnical Engineers Conference 21st – 24th of June 2016, Sibiu, Romania

Geotechnical investigation for determination of causes for occurred deformations of the Aqueduct

B. RUMENOVSKI1*, K. TASEVSKA2, B. JAKIMOVSKI3, T. DIMITRIEVSKI4

1BSc.geotech.eng., GEING Krebs und Kiefer International and others, Skopje, R.Macedonia 2BSc.geotech.eng., GEING Krebs und Kiefer International and others, Skopje, R.Macedonia 3BSc.geotech.eng., GEING Krebs und Kiefer International and others, Skopje, R.Macedonia 4BSc.geotech.eng., GEING Krebs und Kiefer International and others, Skopje, R.Macedonia

ABSTRACT This paper deals with geotechnical investigation works for assessment of factors which led to occurrence of deformations of Skopje Aqueduct – significant monument for Macedonian cultural heritage. The period of construction of the Aqueduct is still undetermined. According some data, the monument was built in the 6th century in the time of the Byzantine , while according to other data, it was built in the 15th century. It is presumed that it was still in use by the end of the 19th century. Based on the performed geotechnical investigations and geophysical surveys on the site, emphasizing the deformed zone of the Aqueduct, as factors for occurrence of deformations were noticed the relatively weak stress-strain properties of the foundation soil, the shallow foundation of the structure, the permanently flooded site, local tectonic and the modifications in the spreading of surface clayey layer, as possible agents for different damaging (sloping) of the Aqueduct pillars.

Keywords: Aqueduct, geotechnical investigations and geophysical surveys, deformed zone

* presenting author

into water supply system, and at the same 1. INTRODUCTION time with high architectural values. The Aqueduct is located on the north of 1.1. The Aqueduct construction the city centre between the Skopje generals Fortress – Kale and the Skupi The Aqueduct is preserved in its entire archaeological site, in vicinity of the city of length which is 385,80 meters long, and it Skopje, Republic of Macedonia. As a has 54 main vaults and 42 so called linear building with an angle in the center “relaxing” vaulted holes placed over the of the construction, the Aqueduct is a pillars for reducing the structure weight. distinctive landscape feature. The lower part of the Aqueduct consists of It is built over a small valley of the Serava 53 square or rectangular pillars whit width River, with the altitude close to 300 of 2,15 meters to 2,24 meters, and 2 side meters, as a part of water supply system ramps – northern and southern, with their that carried water from Skopska Crna foundations. Gora Mountains to Skopje Fortress. Method of building is rich and colourful, The construction date of the Aqueduct is from different kinds of stone and brick. still undetermined. According some data, th The pillars from the oldest construction the monument was built in the 6 century phase are built of river stone in in the period of Roman or Byzantine characteristic rows of brick old format and Empire i.e. the time of the Justinian I (527- partly stone tiles and other fragments in 554 A.D.). But due to similarities in the lime mortar. The facades are of mixed construction method between this masonry, stone and brick in lime mortar, structure and Kurshumli An in Skopje it is with archivolts and outside arches of brick. considered that the Aqueduct is built in the th The Aqueduct as original civil structure, 15 century, period in which the city of provides the opportunity to studying the Skopje intensively started to grow along methods and techniques of building this with building of new Islamic structures – type of construction and used building Turkish baths and mosques. For materials. construction and functioning of such Few construction phases and repairs can facilities huge quantities of pure water be noticed on the building. Most of those were required. It is presumed that it was originate from the end of 19th century and still in use by the end of the 19th century. the beginning of 20th century. After the Second World War, three vaults were destroyed by mines in a military exercise to demonstrate the destruction of bridge vaults. It is presumed that these vaults were reconstructed in 1968 yr.

Figure 2. Aqueduct after the dynamites’ exercise Figure 1. The oldest overview of the Aqueduct The last restoration of the Aqueduct was in Skopje, drawing from year 1883-1884 carried out after the earthquake in Skopje (published by the English archaeologist Arthur in 1963, repairing three arcs and two John Evans, 1885) pillars destroyed due to the earthquake Overall, the Aqueduct have a double role - activity. construction with strictly defined function

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In the central part of the Aqueduct the Special threat to the monument is a risk of construction is not vertical, it is with an earthquakes. The Skopje valley is a inclination to the west which is up to 53 seismically active zone. The estimated risk cm, and there is a very serious problem of indicates а risk of earthquakes from 7 to 9 disturbance the stability and demolition degrees by MCS (risk area of 9 MCS is the section between pillars no. 9 and located at the bottom of the valley). pillars no. 15. The aim of this paper is to present the Also, a part of the foundations are performed geotechnical investigations, threatened by high groundwater level, so which would determine the causes of in rainy periods form small swamp at the occurred deformations of construction, as lowest point along the construction. well as to recommend appropriate activities for its remediation.

Figure 3. Panoramic view of the Aqueduct in Skopje  Performance of geophysical seismic 2. GEOTECHNICAL investigations; INVESTIGATIONS  Performance of investigation boreholes; In March 2014 yr. by the company "Geing  Standard penetration test – SPT test for Krebs und Kiefer International" Ltd Skopje, each borehole; was performed field investigations and laboratory testing on the location of the  Mapping of the investigation boreholes; Aqueduct. They are performed according  Measuring and registering the to methodology which is in accordance appearance and level of groundwater; with the technical norms wildly applied in  Performance of trail pits; Macedonia and in foreign countries, the Sampling non-disturbed, semi-disturbed Macedonian standards as well as the  and disturbed samples from the instructions and recommendations from investigated boreholes; the technical literature. The purpose of performed investigations  Trail pits mapping; and testing is determination the lithological  Cone penetration test – CPT test; structure, with specifically defining the 2.1. Engineering - geological and hydro physical - mechanical and stress - strain - geological site mapping properties of soil materials, for determination the reason of occurred The terrain is composed of younger deformations, as well as establishing the proluvium deposed sediments, composed appropriate activities recommended for of sands and gravels, silty gravel, covered remediation of the object. with clay (Q2prsk). The thickness of these sediments is 5÷10 m; For more detailed presentation of the lithological structure on the location were Under the proluvium sediments there are applied the following investigation works: Pliocene sediments composed of sands  Engineering - geological and hydro - and gravels, silty clayey, marls, geological site mapping; sandstones and conglomerates to depth 89

of 60.00 m. Under these sediments there higher resolution. These surveys are are Miocene - Pliocene marl sediment performed with continuous following of the deeper than 1000 m. litho-physical modifications in the ground and noticing the local tectonic properties The geological investigations on the of the location. The surveys provide more terrain are showing that there is fault with realistic defining the data for physical – direction NE-SW. This profile is not given mechanical and the geotechnical on the engineering-geological map for assemble of the investigated area. Skopje, but is given on the engineering- geological profiles VIII-VIII’ and XII-XII’ (in For registering seismic waves are used the mentioned report from 1963-1964). It vertical geophones of 14 Hz. is estimated that this fault cuts the location 2.3. The interpretation of data from on the damaged part of the aqueduct. refraction profiles 2.2. Performance of geophysical The interpretation of data from refraction seismic investigations; profiles is performed with hodochrones of The seismic investigations are performed P and S waves, thus were determinate the with shallow refraction and reflective following parameters of registered elastic profiles, placed according the investigation environments: purposes.  The values of Vp and Vs seismic The refraction profiling are performed with velocities; 4 profiles with total length of 325 m. The  The physical-mechanical and elastic profile RF-1 is performed with length of dynamical properties, determinate 125 m on distance of 1m (east) from the according the seismic Vp and Vs pillars’ line of the aqueduct, continuously velocities; along the complete length on the  The dynamical properties of materials investigated location. The profile RF-2 is during earthquake; made at the beginning, RF-3 in the middle (zone of modification of the pillars The refraction survey determinates the inclination) and RF-4 at the end of the following contoured and average (in the investigated location. These profiles are bracket) values of seismic waves Vp and performed normally on the line of the Vs of the foundation environments of the aqueduct pillars, each with length of 65 m. aqueduct and its geological basis. The profiles are performed with geophone  High plastic clay, on depth of 1-3 m with distance on 5 m and stimulation of seismic values of Vp=340-450 (400) m/s and waves on 15 m. Vs=125-180 (150) m/s; For more detailed perception of data  Sands and gravels, silty clayey modification from refraction investigations materials on depth of 2-5 m and values it is performed refraction interpretation of of Vp=400-550 (500) m/s and Vs=180- reflective profiles, given in the refraction 250 (220) m/s; profiles RF-5 (located in parallel with RF-1  Sands, gravels, sandy clayey silt on on distance of 5 km toward west) and RF- depth of 8-12 m with values of 6 located in parallel with RF-3 on distance Vp=910-1360 (1100) m/s and Vs=400- of 4 m toward north. The complete length 570 (460) m/s; of these profiles is 190 m.  Sands, gravels and clayey silt on depth With the refraction profiles is reached of 8-23 m, with Vp=1750-2350 (2000) depth of 20-30 m. m/s Vs=650-950 (800) m/s; The reflective profiling are performed in  Sandstones, marlstones and order to provide comparison if the conglomerates deeper than 23 m, with interpretation of the geological structure Vp=2420-2760 (2600) m/s and from refraction surveys with surveys with Vs=1000-1100 (1000) m/s.

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The first three environments belong into  Elastic litho-physical boundaries Quarter younger proluvial sediments between the surface clay layer and (Q2prsk), and the average 4 and 5 of proluvial sandy gravel material and Pliocene sediments (Pl). We should stress between the materials of proluval and out that some of the materials in the Pliocene sediments; middle 3 belong into the surface weaken  The tectonic disturbing and dislocation Pliocene materials. (faults) in geological environment of According the data of refraction profile RF- the terrain; 1 and RF-5, the deeper depth of Quarter From point of view the local tectonic here proluvial sediments (around 12 m) are in are interpreted two tectonic dislocations, the beginning – the north part of the cutting the investigated location of the location (the pillars S1, S2 and S3) near aqueduct. The first dislocation (P1) has the channel Serava. At the final – south spreading NW-SE and cuts the aqueduct art of the location (S20 and S2) its depth is in the zone of the third and the fourth around 6-8 m. Comparing the data from pillar. This dislocation is agent for the the profiles RF-1 and RF-5 (on distance of inclination of the pillars (1-9) of the 5 m), we can conclude that the depth of aqueduct toward east in the first half of the the quarter sediments is reduced for location. The second dislocation (P2) has around 2 m in the west part, actually for direction NE-SW, cutting the zone in the the same distance is increased in the east tenth and eleventh pillar causing part of the location. inclination of the pillars (10-21) toward This conclusion is confirmed with the west in the second part of the location. cross section profile RF-2 and RF-6. On The dislocation (P2) is confirmed with the the profile RF-3 is obtained increasing of geological investigations after Skopje the thickness at the Quarter sediments in earthquake in 1963-1964. the west part, and on the profile RF-4 in The interpreted local tectonic and the the east part of the location. The modifications for spreading the surface appearance of RF-4 can be explained with clay layer are the possible reason for the possible surface or tectonic damaging of variable damaging (hobbling) of the the surface Pliocene sediments. aqueduct pillars. Due to this it should pay According the values of seismic waves, attention to the modifications of the the first elastic environment – the surface physical – mechanical properties of the layer with depth of 2-3 m can be classified clay during the different weather as archeological cultural layer. conditions and the effects of clay swelling. The interpretation of reflective profiles determinate:

Table 6. Interval values of elastic dynamical parameters Proluvium Proluvium Proluvium Pliocene sediments sediments sediments sediments Parameter (Pl) (Q2prsk) (Q2prsk) (Q2prsk) H (m) 1-3 2-5 8-12 25-60 Vp (m/s) 340-450 400-550 910-1360 1750-2750 Vs (m/s) 125-180 180-250 400-570 650-1100  (kN/m3) 15-16 17-18 19-20 21-23

din 0.42-0.40 0.38-0.37 0.38-0.39 0.42-0.40 Edin (MPa) 68-148 165-315 855-1840 2570-7950 Gdin(MPa) 25-55 60-115 375-660 905-2840 Kdin(MPa) 142-247 230-405 1100-2790 5350-13250

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2.4. Cone penetration test – CPT test;  Resistance of pipe attrition; On the investigated location are performed  Resistance of attrition of cone and pipe; tests of static penetration (CPT – test). The test of static penetration is performed The classification of soil materials is with penetrometer type Holland 10 t with performed according the cone Type: Dutch Mantle Cone D=35.7 recommendations of Robertson et al, 1990 mm, A=10 cm2. The measurements are which is showed in following pictures and performed in the following phases: tables.

 Cone resistance; Zone 1 Sensitive, fine grained 2 Organic materials 3 Clay 4 Silty clay to clay 5 Clayey silt to silty clay 6 Sandy silt to clayey silt 7 Silty sand to sandy silt 8 Sand to silty sand 9 Sand

Cone resistance Q (kN) Q resistance (kN) Cone 10 Gravely sand to sand 11 Very stiff fine grained* 12 Sand to clayey sand*

Attrition ratio (%), Rf * Over consolidated or cemented

Table 7. Classification of soil materials 2 Depth [m] Mv [kN/m ] Classification Description Robertson (1990) Robertson (1990) CPT-1 0.25-2.00 4500 CI/MI Clay Very compact, fine grained, over consolidated or 2.00-2.50 17700 ML cemented materials CPT-2 0.25-1.75 6500 CI/MI Clay Very compact, fine grained, over consolidated or 1.75-2.50 12000 ML cemented materials CPT-3 0.50-3.00 4300 CI/MI Clay Very compact, fine grained, over consolidated or 3.00-3.75 12000 ML cemented materials CPT-4 0.25-3.50 2618 H, CI/MI Clay, organic clay, humus 3.50-4.00 57750 CI/MI Clay Very compact, fine grained, over consolidated or 4.00-8.50 16125 SFs cemented materials CPT-5

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0.75-1.00 750 H Organic materials 1.00-2.50 8250 CI/MI Clay Very compact, fine grained, over consolidated or 2.50-4.00 12375 ML cemented materials Very compact, fine grained, over consolidated or 4.00-4.50 37500 SFs cemented materials CPT-6 0.00-1.00 300 CI/MI Clay, organic clay 1.00-3.25 3000 CI/MI Clay 3.25-4.00 52500 SFs Sandy silt to clayey silt CPT-7 0.25-1.00 1750 CI/MI Clay Very compact, fine grained, over consolidated or 1.00-2.25 39300 SFs cemented materials CPT-8 0.25-0.75 1500 CI/MI Clay Very compact, fine grained, over consolidated or 1.75-1.50 65000 SFs cemented materials 2.5. Performance of investigation BH-1 to BH-10. The investigation drilling is boreholes; performed geomechanical point of view, On the investigated site are performed 10 with dry drilling that allow getting quality (ten) investigation boreholes, each with core 100%. 10.00 meters depth. The investigation The data for the depth of the investigation drilling is performed with two drilling boreholes, type, number and depth of machines (GAK 300 and GDR 150) on each sampling, as well as the ground previously defined locations marked from water appearance are given in table no. 8.

Table 8. Review of investigation boreholes Borehole Final depth Appearance of Level of Sampling [m] groundwater groundwater Sampling BH-2 10.0 / / 3 BH-3 10.0 6.30 / 3 BH-4 10.0 / 6.30 4 BH-5 10.0 / 8.30 4 BH-6 10.0 / 6.30 6 BH-7 10.0 8.30 / 2 BH-8 10.0 8.30 / 4 BH-9 10.0 / / 3 BH-10 10.0 / / 2

During the investigation drilling are the laboratory tests. The compression preformed SPT tests, for quality estimation module for the incoherent materials is of the foundation compactness. The tests determinate through the SPT (Standard are used for orientation qualification of the penetration test) in table no. 9. mechanical parameters of the materials (φ, c and Mv) as comparative indicators of Table no. 9 Review of performed SPT tests

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Borehole Depth Cone penetration Hits number Corrected number of hits Compactness/c onsistency Compressibility modulus Angle of internal friction Mv (m) (cm) N N’ N’’ N N / (°) kor def (kPa) φ 1.600÷1.904 30.4 29 20 / / 20 Solid 12500 / Very BH-1 3.800÷3.900 10 30 21 / 64 64 48300 43 compact 7.700÷8.004 30.4 21 15 / / 15 semisolid 10000 / 1.700÷2.004 30.4 30 21 / / 21 solid 13000 / 3.200÷3.330 13 30 21 / 49 49 compact 37800 40 BH-2 5.200÷5.504 30.4 14 10 / / 10 semisolid 7500 / 7.500÷7.804 30.4 17 12 / / 12 semisolid 8500 / 2.300÷2.450 15 30 21 / 43 43 compact 33600 39 medium 4.000÷4.210 21 30 21 / 30 30 24500 36 compact BH-3 6.200÷6.504 30.4 13 9 / / 9 semisolid 7000 / medium 8.500÷8.804 30.4 26 18 / / 18 16100 33 compact 1.600÷1.904 30.4 27 19 / / 19 solid 16800 / 2.600÷2.770 17 30 21 / 38 38 compact 30100 38 4.800÷5.104 30.4 11 8 / / 8 soft 6500 / BH -4 medium 7.000÷7.230 23 30 21 / 28 28 23100 36 compact Medium 8.000÷8.210 21 30 21 / 30 30 24500 36 compact 2.200÷2.504 30.4 30 21 / / 21 solid 13000 / 5.000÷5.280 28 30 21 / 23 23 solid 14000 / BH -5 medium 7.800÷8.104 30.4 24 17 / / 17 15400 32 compact 1.800÷2.104 30.4 22 15 / / 15 semisolid 10000 / BH 6 3.500÷3.804 30.4 24 17 / / 17 semisolid 11000 / 7.200÷7.504 30.4 20 14 / / 14 semisolid 9500 / 1.700÷2.004 30.4 30 21 / / 21 solid 13000 / BH -7 medium 7.000÷7.240 24 30 21 / 27 27 22400 35 compact BH -8 1.600÷1.880 28 30 21 / 23 23 solid 14000 / 1.500÷1.630 13 30 21 / 49 49 compact 37800 40 BH -9 medium 5.600÷5.840 24 30 21 / 27 27 22400 35 compact 1.500÷1.804 30.4 13 9 / / 9 semisolid 7000 / BH-10 5.000÷5.304 30.4 15 11 / / 11 semisolid 8000 / 2.6. Physical-mechanical features of the laboratory testing, i.e. defining the physical materials and its classification – mechanical properties of the present In order to obtain more representative materials on the field and the location physical – mechanical properties of the under the aqueduct. terrain depending on depth, it were According the performed classification performed certain type and scope of based on the site mapping and the investigations boreholes from which were laboratory tests we can conclude that on taken representative samples for further the mentioned location there are the

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following types of materials with physical – As reasons for appearance the mechanical properties as given bellow. deformations of the Aqueduct are the following: Surface layer of clays – CI/MI  The local tectonic and the modification This material is registered on the terrain in the clayey surface layer are the surface along the complete profile on the possible reason for the variable investigated location with maximal layer inclination to the west which is up to 53 thickness of 3.00 m. This layer is cm. Thus, it should pay attention to the composed of medium plastic silty clays in modification of physical – mechanical semi-solid to solid consistent condition properties of the clay during different and covered with humus layer with weather conditions and to the effects of maximal thickness of 1.00 m. The physical clay swelling; – mechanical properties are given as it follows:  The relatively low deformable   c Mv properties of the soil layer where is the Mg/m3 [°] kPa kPa foundation (especially during presence 1.81 16.3÷16.6 13.8÷15.0 7400 of water); Silts and silty sands – ML, CL/SFs,  The relatively shallow foundation of the facility; SFs/ML, SFs  Constantly flowing terrain (creation of These materials are registered under the “lakes” and swamp zones) surface layer of clays. They are classified as low plastic silts, clayey and silty sands 4. CONCLUSIONS and sandy silts. The physical – mechanical properties are given as it Although the Aqueduct in Skopje is not follows: generally known and appreciated by the   c Mv public, the consensus is growing that the Mg/m3 [°] kPa kPa Aqueduct and its surrounding area are 1.81 16.3÷16.6 13.8÷15.0 7400 unique and have an important historical, architectural and esthetical value. Silts and silty sands – GP, GFs From geological point of view the terrain In the lower layers on the location to the on the investigated location is composed final depth there are materials like low of quarter sediments represented with grained and silty sandy medium to well clayey silty fraction creating the upper compact gravels. layers and silty sand and gravel, partially   c Mv clayey deposits in the lower layers. Under 3 Mg/m [°] kPa kPa the Quarter sediments there are Pliocene 1.8 16.3÷16.6 13.8÷15.0 7400 sediments composed of sands and gravels, silty clayey, marls, sandstones 3. CAUSES FOR APPEREANCE and conglomerates to depth of 60 meters THE DEFORMATIONS OF THE and under that there are Miocene FACILITY Pliocene marl sediments on depth of 1000 Based on the performed geotechnical and meters; geo-physical investigations on the From hydro-geologic point of view the location, with special review of the investigated site belongs into the group of deformed zone of the Aqueduct we can low to well yield terrains where is conclude the following: developed compact type of aquifers in The aqueduct is founded on foundations sediments characterized with inter with average width of 2 x 2 meters in the granular porosity. Considering the layer of silty clay with medium plasticity, geological structure of the field, especially and foundation depth of 0.70 meters to the upper parts, we should stress out on 1.30 meters from terrain elevation. the location and the wider region is

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present contemporary geologic process of rehabilitation of the Aqueduct in Skopje permanently washed terrain (creation of and its environment”. “lakes” and swamp zones); Master Urban Plan Skopje, Institute of From geo-tectonic point of view the town planning and architecture – investigated location belongs into area Skopje; Polservice Consultants, with maximal intensity of VIII and IXº Warsaw; Doxiadis Associates – according MCS. The strongest earthquake Consultants on Development and is noticed in 1963 with intensity of IXº Ekstics, (1965) according MCS in Skopje epicentre area, Lenche Jovanova, “Skupi – Colonia Flavia followed with aftershocks with own local Scupinorum”, Skopje (2008) epicentre on depth of 5 km; Kosta Balabanov, Antonie Nikolovski, On the location are performed 10 (ten) Dimitar Kjornakov, “Monuments of investigation boreholes each with depth of culture in Macedonia”, Skopje (1980) 10.00 meters, 8 (eight) tests of static penetration SPT-tests, 8 (eight) trial pits near the most damaged pillars and geophysical seismic survey with total length of 325.00 meters, refraction surveys and 180.00 meters reflective surveys; The location has relatively heterogeneous composition concerning the classification and physical – mechanical properties of the present materials. The surface layer is composed of silty sandy medium plastic clays covered with humus and clayey humus cover. The maximal spreading depth of the layer is 3 m. Under this layer to the final investigation depth there are sandy silts, silty sands and gravels, as well as low grained gravels in the zone around river Serava;

ACKNOWLEDGEMENTS The authors of this paper would like to thank the company "Geing Krebs und Kiefer International" Ltd Skopje, and to the Ministry of Culture, Skopje, for the support while making the researches for the Aqueduct and the opportunity to participate on this Conference.

REFERENCES Geing Krebs und Kiefer International Ltd Skopje (2014) “Elaborate for geotechnical investigations and laboratory testing on the location of the Aqueduct in Skopje”. Ministry of Culture, Skopje (2011) “Strategic plan for preservation and

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